Internal combustion engines may recirculate a portion of the exhaust gas to the engine intake to mitigate high engine combustion temperatures and to reduce formation and emission of NOx gases. Conventionally, during certain engine conditions, exhaust gas recirculation (EGR) may be stopped in order to maintain vehicle drivability. For example, at very high engine loads or full throttle, EGR may be shut off in order to increase oxygen intake to the engine and to meet the demanded engine load. As a further example, EGR may be shut off during engine idle conditions to reduce rough engine idle due to unstable combustion.
The inventors herein have recognized potential issues with the above conventional approaches. Namely, after EGR is switched off, the oxygen concentration in the exhaust gas stored in the EGR system (e.g., exhaust manifold, and/or exhaust recirculation line) may be very low. Accordingly, when EGR is resumed, flow of exhaust gas with low oxygen concentration levels may be delivered to the engine cylinders, which may starve the engine of oxygen and cause engine operation and vehicle drivability problems such as misfires, stumbling, and the like.
One approach that addresses the aforementioned issues is a method for an engine, comprising, in response to an EGR valve closing, determining an EGR oxygen content, and purging an EGR system when the EGR oxygen content is less than a threshold oxygen content.
In another embodiment, a method for a vehicle engine may comprise purging an EGR system, including opening an EGR valve, when the EGR valve would otherwise be closed, based on a measured oxygen concentration of the EGR system being less than a threshold oxygen concentration.
In another embodiment, an engine system may comprise an EGR system, comprising an EGR valve, and a controller, including executable instructions to, in response to an EGR valve closing, determine an EGR oxygen content; and purge an EGR system when the EGR oxygen content is less than a threshold oxygen content.
The above advantages as well as other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.